MATOKEO YA MITIHANI KIDATO CHA PILI 2025
This
summary provides an overview of the provided lesson notes on Chemical Kinetics
for Advanced Level. Fundamental Concepts
- Chemical
Kinetics: The
study of reaction rates and the mechanisms by which reactions occur.
- Reaction
Rate: Defined
as the speed at which reactants convert to products, measurable by the
rate of reactant disappearance or product formation.
- Average
vs. Instantaneous Rate: Average
rate tracks concentration changes over a specific time interval, while
instantaneous rate represents the exact speed at a specific microscopic
moment.
- Law
of Mass Action: At
constant temperature, the reaction rate is directly proportional to the
product of the molar concentrations of the reacting species.
Reaction
Orders and Rate Laws
- Rate
Law Expression: A
mathematical expression relating the observed reaction rate to the
concentrations of reacting species.
- Order
of Reaction: The
sum of the powers to which concentration terms are raised in the rate law
expression; it is determined experimentally.
- First-Order
Reactions: The
rate is proportional to the first power of a reactant's
concentration. The half-life is independent of the initial
concentration.
- Second-Order
Reactions: The
rate is proportional to the second power of concentration. The
half-life depends on the initial concentration.
- Pseudo-Order
Reactions: Occur
when one reactant is in large excess, making the reaction appear to have a
different order than it actually does.
Mechanisms
and Collision Theory
- Reaction
Mechanism: A
sequence of elementary steps converting reactants to products.
- Rate-Determining
Step: The
slowest step in a mechanism, which dictates the overall reaction speed.
- Collision
Theory: For
a reaction to occur, molecules must collide with sufficient energy
(activation energy) and correct orientation.
- Arrhenius
Equation: Describes
the relationship between the rate constant, temperature, and activation
energy ($k = Ae^{-E_a/RT}$).
Factors
Affecting Reaction Rate
The
rate of reaction is influenced by concentration, physical state (particle
size), pressure, light, temperature, and catalysts. Catalysts speed up
reactions by providing an alternative pathway with a lower activation energy
without being consumed.
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